1. Field of the Invention
The present invention relates to a process for the manufacture of organosilicon products by hydrosilation in the presence of a catalyst.
2. Background of the Art
Hydrosilation reactions for syntheses of organosilicon, i.e., organosiloxane or organosilane, products are well known and generally involve catalyzed hydrosilation of an unsaturated compound with a silane or a silicon polymer containing reactive silanic-hydrogen and/or hydrogen-siloxy units in the presence of a precious metal catalyst, e.g., platinum (Pt), rhodium and palladium. When traditional homogeneous precious metal catalysts, e.g., chloroplatinic acid (CPA) solution and Karstedt's catalyst, are used, precious metal catalysts remain in organosilicon product-containing reaction media, e.g., siloxane or silane streams, causing significant precious metal waste, high color in organosilicon products, and black particle formation due to slow precious metal precipitation causing customer complaints of organosilicon products such as cosmetic and personal use products.
In certain organosilicon products, there is a low color specification. For example, a hydrosilylation product of triethoxysilane with 1-octene needs to have a color of less than 30 pt/co (as determined by ASTM D1209). However, the existence of precious metal catalysts such as platinum in the product causes product color, i.e., having a color of much more than 30 pt/co. As a result, heavy distillation is needed to remove precious metals and to reduce product color. This additional heavy distillation step not only reduces product yield but also significantly increases final product cost.
Homogeneous precious metal catalysts, e.g., chloroplatinic acid solution invented by Speier et al. (U.S. Pat. No. 2,823,218), platinum siloxane solution invented by Karstedt (U.S. Pat. No. 3,775,452), chloroplatinic acid reaction product (U.S. Pat. No. 3,220,972), etc., are commonly used in hydrosilation reactions for syntheses of organosilicon, i.e., organosiloxane or organosilane, products. As a result, precious metals remain in final organosilicon products, causing significant precious metal waste, high color in organosilicon products, and black particle formation due to slow precious metal precipitation causing customer complaints of organosilicon products such as cosmetic and personal use products.
Use of heterogeneous precious metal catalysts in hydrosilation reactions is known. As early as in 1950's, Wagner et al. have used platinum black, platinized silica gel, and platinized asbestos (U.S. Pat. No. 2,632,013), platinum on charcoal (U.S. Pat. No. 2,637,738), and platinum on gamma alumina (U.S. Pat. No. 2,851,473) in hydrosilation reactions to make organosilane products.
U.S. Pat. No. 7,038,001 teaches a method for preparing silicone oils by hydrosilation of polyorganohydrosiloxanes with units containing at least one hydrocarbon ring including an oxygen atom, in the presence of a commercial heterogeneous catalyst (e.g., platinum on charcoal or carbon black, platinum on alumina, etc.). The use of heterogeneous catalyst could (1) minimize ring open polymerization during hydrosilation and devolatilization and produce constant low-viscosity product; (2) reduce isomerization of unsaturated synthon; and (3) reduce product platinum content, color and turbidity. However, the method disclosed in this invention is not for general hydrosilation reactions to make organosiloxane and organosilane products. Moreover, the method disclosed in this patent employs devolatilization of the silicon oil, which is not required in the present invention.
U.S. Pat. No. 4,533,744 teaches the synthesis of a new heterogeneous hydrosilation catalyst having platinum atoms anchored onto a hydroxylated oxide of silicon or aluminum by Pt—S linkages through sulfur organo siloxy groups, and the catalyst can be reused. U.S. Pat. No. 4,064,154 teaches the preparation of a catalyst carrier substance by reacting an inorganic particulate solid having surface hydroxyl groups with an organosilicon compound containing sulfur. The carrier can be converted to a supported catalyst by reaction with a compound or complex of platinum or rhodium. The catalyst can be recovered and recycled and is useful for hydrosilation reactions. U.S. Pat. No. 5,347,027 teaches an electroless process for making a hydrosilation catalyst by contacting a base metal with a chemical cleaning agent and simultaneously or sequentially treating said base metal under reducing conditions with a noble metal-containing material, and the catalyst is recoverable and reusable. U.S. Pat. No. 6,177,585 teaches the synthesis of a bimetallic heterogeneous platinum catalyst comprising an active hydrosilating metal such as platinum in elemental or compound form, and a surface segregating metal such as copper in elemental or compound form on a support. The bimetallic catalyst showed significantly improved catalytic performance compared to the single precious metal catalyst. These four patents disclose methods to synthesize new heterogeneous precious metal catalysts for hydrosilation reactions, and the catalysts are recoverable and reusable. However, these patents did not teach applications of heterogeneous catalysts as an effective way to improve organosilicon product quality (e.g., remove color and eliminate black particle formation) and simplify organosilicon manufacturing process (e.g., eliminate the step of heavy distillation for precious metal removal).
U.S. Pat. No. 6,087,523 teaches the use of commercial Pt/Al2O3 heterogeneous catalyst in hydrosilation to make organosilane. The invention specifically refers to the hydrosilation of unsaturated reactants where the unsaturation is in the internal portion of the reactant's structure, for example, as in cyclopentene and cyclohexene.
U.S. Pat. No. 6,100,408 teaches the preparation of 3-glycidyloxypropyltrialkoxysilanes from allyl glycidyl ether and trialkoxysilane via platinum-catalyzed hydrosilation. The catalyst used was self-synthesized heterogeneous platinum(0) on a nonmetallic support, and the process is preferred at a continuous fixed-bed process. This invention specifically refers to preparation of 3-glycidyloxypropyltrialkoxysilanes and no other organosilicon products are included.
U.S. Pat. No. 5,206,402 teaches a process for preparation of omega-alkenylchlorosilanes. The process comprises reacting a mixture comprising an α,Ω-diene and an organohydrosilane in the presence of a supported platinum catalyst. A preferred process is run as a continuous process employing a fixed-bed of silica gel supported platinum catalyst. The inventors have discovered that migration of the unsaturated bond from a terminal to an internal position in the desired silicon-bonded group can be reduced in the presence of a supported platinum catalyst and with controlled mole ratio of α,Ω-diene to organohydrosilane.
U.S. Pat. No. 5,270,424 discussed a similar matter for reaction of a silicon compound having SiH groups with a diene having at least 5 carbon atoms. The use of Pt/Silica heterogeneous catalyst could reduce the content of isomers resulting from migration of double bond to internal position.
U.S. Pat. No. 6,350,824 teaches the application of a newly designed continuous hydrosilation reactor, including the use of heterogeneous precious metal catalysts in fixed-bed mode. Numerous examples of hydrosilation reactions were provided and very short residence times in the reaction zone were required to achieve complete conversions according to the invention. Again, the patent did not present the applications of heterogeneous catalysts as an effective way to improve organosilicon product quality (e.g., remove color and eliminate black particle formation) and simplify organosilicon manufacturing process (e.g., eliminate the step of heavy distillation for precious metal removal).